Internal-combustion engine piston



June 27, 1950 L. DUNCAN INTERNAL-COMBUSTION ENGINE PISTON Filed March 20, 1948 FIG.- 2

FIG-I FIG.- 4

FIG-3 FIG-5 INVENTOR LANE DUNCAN @Aj/ M4 a Wm ATTORNEYS Patented June 27, 1950 UNITED -':STATES PAT-ENT- OFFICE.

'INTERNAL -COMBUSTIONENGINETISTON Lane-DuncamLos Angeles, Calif.

Application March'20, 1948, 'Serial'No.16',1-15

c1. 12s .i9s)

1 Claim.

The invention relates to a-novel and improved piston for an internal-combustion engine. It relates more particularly to a piston especially adapted for service undersevere temperature and pressure conditions, suchas in two cycle motors for speed boats, or the like.

As is well known to those skilled inthe art, aluminum base alloys are widely used for pistons. The relativel low specific gravity-of such alloys, as compared with the ferrous metals, reduces the inertia to be overcome at each reversal of piston direction which of course may occur as often as several thousand times per minute. In addition, the relatively high thermal conductivity of aluminum-is of material assistance in preventing overheating of the gases being compressed in the combustion chamber, with consequent prevention of carbon formation and pre-ignition knock.

Aluminum and its alloys have a relatively low melting point as compared with the cuprous and ferrous metals. Pure aluminum melts at 1220 F., and additions of the usual alloying elements reduces this in familiar fashion, so that in the well knownalloys of aluminum with silicon, copper, or other alloying additions incipient fusion of eutectics may be encountered anywhere above about 1000" F.

In'h-i'gh speed internal combustion engines, and especially in small engines where low total weight is practically anecessity, for example in racing craft, cooling facilities are not elaborate, and may even be somewhat inadequate, so that the. piston, and moreparticularly the piston head, may reach such a high temperature in high speed operation that incipient fusion is encountered on the piston head.

An object of the present invention is to provide a novel and improved piston head-structure for the prevention of incipient fusion of the piston head.

A further object of the invention is to provide novel and improved means for increasing the thermal conductivity of the piston head, so as to conduct the heat from the local hot spot causing more uniform expansion, and less distortion.

Other objects and advantages will be apparent from a study of the following description, in conjunction with the accompanying drawings, in which:

Fig. 1 is a vertical section view through a piston and cylinder assembly wherein the piston exemplifies one embodiment of my invention;

Fig. 2 is a top plan view, looking down on the piston head;

Fig. 3 is a fragmentary sectional view similar carbonization of the piston material.

. 2 to Fig. 1, but illustrating yet another'embodiment of my invention; r Y

Fig. 4;: is-a top plan-view, looking down on---Fig. 3; while,

2: Figs. 5 and 6 aresectiona1 and planrviewsrescribed, as the invention obviously may take varir tion, the-scope of the present inventiorrbeing defined in the appended claim.

The embodiment-of the invention shownin Fig.

1 is a pistonadapted for 'use in a two cycleengine. The piston i0 is the-usual cup shaped aluminum alloy casting having a head-l l and depending annular skirt [2. The present invention is'incorporated entirely in the head structure,- and further description of other conventional piston "characteristics is deemed unnecessary.

Intwo .cy'cl'e operation the inrush of fresh fuel mixture materially aids in expelling theburned ases from the combustion chamber 13, and the consistingof a raised barrier I4 extending transversely of thepiston head between the inlet and.

exhaustports in thecylinder head I5. The inrushing gas isdefiected upwardly in the direction of the full line arrows, whil the burned gases are driven outwardly as indicated by the broken line arrows. vSuch-baiflameanshas been known'heretoforaand thestructureso far described is-con- Ventional. I

Those skilled in the design and operation of internal combustion engines are familiar with the fact that the hottest point on the piston head is at the extreme top edge of the bafile toward the intake ports, and consequenly in continued high speed engine operation the temperature on the corner Ma of the bafiie 14 tends to induce a certain amount of preliminary melting and local This increases the tendency towards pre-ignition before the piston reaches the timed firing point, and, if long continued, materially reduces the strength of the piston head. Carbonization on the head further injuriously affects the heat conductivity of the head so that the disadvantages multiply. Overheating of the head causes over expansion of the upper skirt portion, so that the piston may scuff or wear rapidly in this region.

To remedy these defects I have provided insert means, forming a portion of the piston head, and disposed in the danger zone, the insert being formed from a metal of considerably higher melting point, and also a higher thermal conductivity, than that of the aluminum base alloy from which the piston is fabricated. The insert, for example, may be of commercially pure copper having a melting point of about 1950 F., and a thermal conductivity almost twice that of aluminum or its usual alloys.

As a consequence, th tendency towards incipient fusion of the piston head is entirely eliminated, while the favorable characteristics resulting from the use of an aluminum piston are practically completely retained. The zone where the highest temperature is developed with a specific piston and cylinder head design is usually determinable from an examination of an all aluminum piston head after a period of use, and the desirable location for my novel insert is then apparent.

Referring again to the drawings and particularly to Figs. 1 and 2, the insert I6 is a strip of copper integrally cast in the aluminum alloy of the piston head. For the purpose of securely retaining the insert in place, it is provided with keying means for tight engagement with the solidifying aluminum during the casting thereof. In the present instance the insert is provided with undercut projecting fingers 16a. around which the molten aluminum alloy metal flows and then solidifies.

,Any tendency towards localization of hot spots in the neighborhood of insert [6 is offset by the relatively high heat conductivity of insert which carries the heat downwardly from the upper piston surface and distributes it deeply within the head.

A further embodiment of the invention is shown in Figs. 3 and 4, and consists of an insert in the form of a pad of copper i1 overlying a substantial portion of the crest of baiile 18. Here too keying projections Ila extend downwardly into the head to distribute the heat, and to key the insert in place. In this embodiment the total weight of the piston is slightly increased, since the specific gravity of copper exceeds that of aluminum, but the piston head will run cooler than that of the previously described embodiment, even under more severe temperature conditions, and some weight may be saved elsewhere in the piston if desirable or necessary.

Yet, another embodiment of the invention is shown in Figs. 5 and 6. In this embodiment the insert has a plurality of depending ribs or fingers 19 a which extend completely through the metal of the piston head and project into the hollow interior of the head. In this arrangement the projections are cooled by fuel which enters the crankcase before being transferred to the combustion chamber and the insert I9 will run still cooler than the embodiment shown in Figs. 3 and 4. If, as is usual, the piston of Figs. 5 and 6 is made by a casting process, the exposed inner end of projections, ribs, or fingers lea. may be imbedded in the sand core, or gripped in a metal core section, and the aluminum alloy cast around it in customary fashion.

So far in the present description the piston has been described as preferably fabricated from an aluminum base alloy. In recent years magnesium and its alloys have been developed to such extent that they are at present available, and to some extent have been commercially used, for pistons for internal combustion engines. The problems of incipient fusion are present to a slightly greater extent with magnesium alloys than with aluminum alloys since magnesium has a slightly lower melting point than aluminum, and also a lower thermal conductivity. In the appended claim I have used the term light metal to comprehend both aluminum and its alloys, and magnesium and its alloys.

Vfhat I claim is:

l. A piston for an internal combustion engine, said piston formed practically completely from a light metal alloy and having an annular skirt and a head integral therewith and extending completely transversely acros the upper portion of said skirt, an insert formed of a metal having a higher melting point than said light metal alloy, said insert being carried by said head and having a surface portion thereof exposed exteriorly of said head to the combustion chamber of said engine, and having depending portions thereof extending completely through said head into the piston interior, said depending portions each having a wall portion which has heat transfer contact with the said light metal alloy portion of said head.

LANE DUNCAN.

REFERENCES CITED The following references are of record in th file of this patent:

France May 2'7, 1939 

